JP2712549B2 - Passivation film for MOS semiconductor device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a passivation film for a resin-encapsulated MOS semiconductor device, and more particularly, to a passivation method that is inexpensive and can simplify the process. It is.

(Prior Art) As the area of a semiconductor chip increases, sliding of wires and passivation cracks due to thermal stress due to a difference in thermal expansion coefficient between the sealing resin and the semiconductor chip have become a problem. The problem is that a large internal stress, which is generated when depositing an inorganic passivation film such as a silicon nitride film on a semiconductor chip, causes stress to be applied to the semiconductor element. To solve this problem, it has been studied to apply polyimide on the passivation film to absorb the stress.

However, this method is complicated since a step of applying polyimide is required after the passivation of the inorganic film is formed. Further, the use of polyimide directly for the passivation film has been performed in the field of bipolar ICs, but has not been used in the field of MOS semiconductors due to problems such as leakage current and corrosion of wiring.

In order to solve the above-mentioned problems, it is important to prevent moisture and ionic components from entering the semiconductor chip, and to apply polyimide having excellent adhesion to both the semiconductor chip and the sealing resin. Thus, the formation of a passivation film made of an inorganic film can be omitted.

In view of such circumstances, the present inventors have conducted many synthesis experiments on many polyimide resins, and studied in detail the relationship between the raw material components and the adhesion between the sealing resin. US Patent No. 3,179,614 (du Pont) as polyimide
Description, CESroog, "Polimides", J. Polym. Sci .: Maromo
l.Rev., 11 , 161-208 (1976), NAAdrova etal, Dokl.Aka
Various types have been proposed as shown in d. Nauk. SSSR, 165 , 1069, (1965). However, very few are actually used in practice. Reported or commercially available are pyromellitic dianhydride,
There are only benzophenone tetracarboxylic dianhydrides or biphenyl tetracarboxylic dianhydrides, diaminodiphenyl ethers and diaminodiphenylmethane as raw materials. However, since the adhesion of these polyimides to the sealing resin becomes almost zero after the pressure cooker test, there is no effect of preventing leakage current and corrosion of wiring.

However, the present inventors have further conducted synthetic experiments, and when using a polyimide obtained from a specific aromatic diamine and tetracarboxylic acid, the adhesion to the sealing resin is greater than that of a conventional polyimide, The present inventors have found that the use of such a polyimide is effective in preventing corrosion of wiring of a semiconductor chip, and have reached the present invention.

[Problem to be Solved by the Invention] An object of the present invention is to provide an inexpensive passivation method using polyimide which can be used in a MOS semiconductor as described above.

[Means for Solving the Problems] The object of the present invention is achieved by the following configurations.

(1) A passivation film used in a resin-sealed MOS semiconductor device, wherein the passivation film is made of polyimide, and the polyimide has a main dispersion (α dispersion) lower than the main dispersion by dynamic viscoelasticity measurement. A passivation film for a MOS semiconductor device, which has a sub-dispersion (β dispersion) generated at a temperature and is made of polyimide whose β dispersion temperature is equal to or lower than a post-curing temperature of a sealing resin.

(2) The polyimide having a main dispersion (α dispersion) by dynamic viscoelasticity measurement of a polyimide forming the stress absorbing film and a sub-dispersion (β dispersion) generated at a temperature lower than the main dispersion according to (1) above, 3,4,3 ', 4'-benzophenonetetracarboxylic acid and 3,4'-diaminodiphenyl ether, 3,4,3', 4'-diphenylethertetracarboxylic acid and 3,4'-diami 3,4,3 '2,4'-benzophenonetetracarboxylic acid and 2,2-bis (4-aminophenoxy) diphenylpropane, 3,4,3 ', 4'-diphenylethertetracarboxylic acid and 2,2-bis (4-aminophenoxy)
Diphenylpropane, 3,4,3 ', 4'-benzophenonetetracarboxylic acid and 2,2-bis (4-aminophenoxy)
Diphenylhexafluoropropane and 3,4,3 ', 4'
A passivation film for a MOS semiconductor device, wherein the passivation film is at least one selected from diphenyl ether tetracarboxylic acid and 4,4'-diaminodiphenyl ether.

In the present invention, the MOS semiconductor device has a basic structure of a three-layer structure of an insulating film made of metal and oxide and a semiconductor. For this reason, since the voltage applied to the gate, which is the control electrode of the MOSFET, is applied via the insulating film, the element can be controlled with an extremely small current. For this reason, if the leakage current of the passivation film for protecting the upper part is large, the semiconductor element may malfunction as a noise component. Further, if there is no effect of suppressing the movement of chlorine ions, corrosion of aluminum used for wiring cannot be prevented.

A passivation film made of an inorganic film such as silicon nitride has a small leakage current and a large effect of suppressing the movement of ionic components. However, since a large internal stress remains when the passivation film is deposited, the device characteristics of the semiconductor device change. In addition, the wiring metal slides, and the internal stress causes cracks in the passivation film and the interlayer insulating film. It has been conventionally studied to apply polyimide as a stress absorbing film on a passivation film. However, such a method is complicated because a process of pattern processing of polyimide is added after the formation of the passivation film.

By using the polyimide having a specific structure of the present invention as a passivation film, it is possible to expect an effective effect of stabilizing leak current, preventing corrosion of wiring, and preventing cracks in an interlayer insulating film.

The polyimide used to form the stress-absorbing film used in the present invention is a polyimide having a main dispersion (α dispersion) measured by dynamic viscoelasticity and a sub-dispersion (β dispersion) generated at a temperature lower than the main dispersion. Yes, and may be anything as long as it is made of polyimide whose β dispersion temperature is equal to or lower than the post cure temperature of the sealing resin,
Preferably, a specific tetracarboxylic acid and a specific diamine compound are selectively combined and reacted in a polar solvent to form a varnish of a polyimide precursor, and then the varnish of the polyimide precursor is used as a semiconductor chip. It can be obtained by coating on the substrate, performing heat treatment in the range of 200 ° C. to 400 ° C., and performing dehydration condensation.

The passivation-forming polyimide of the present invention has a peak of the loss elastic modulus due to β dispersion at a lower temperature in addition to the main dispersion (α dispersion) in the dynamic viscoelasticity measurement. This β
The peak of the loss modulus due to dispersion means that polyimide can cause stress relaxation in this temperature range, and by setting the temperature of this peak lower than the post-curing temperature of the sealing resin, It is possible to alleviate distortion generated during molding during resin post-curing.

Further, from the viewpoint of the heat resistance of polyimide, those composed of aromatics are preferred. Such polyimides include, for example, 3,4,3 ', 4'-benzophenonetetracarboxylic acid and 3,4'-diaminodiphenyl ether, or 3,3
Examples thereof include those synthesized from 4,3 ', 4'-biphenyltetracarboxylic acid and 3,4'-diaminodiphenyl ether. These polyimides have an α dispersion in the range of 250 ° C. to 400 ° C. and a β dispersion at 170 ° C. or lower. More preferred are, for example, 3,4,3 ',
4'-benzophenonetetracarboxylic acid and 2,2-bis (4
-Aminophenoxy) diphenylpropane, or 3,4,
3 ', 4'-Benzophenonetetracarboxylic acid and 2,2-bis (4-aminophenoxy) diphenylhexafluoropropane are listed, and these polyimides have an α dispersion of 25.
It has a β dispersion in the range of 0 ° C. to 400 ° C. and occurs at 150 ° C. or less.

If a polyimide having an α-dispersion of less than 250 ° C. is used, the heat applied at the time of joining the semiconductor element and the lead wire exceeds the α-dispersion temperature of the polyimide. It is not preferable because it causes.

Further, the polyimide in the present invention may be composed of only one kind of tetracarboxylic dianhydride and diamine, or may be a copolymer of several kinds or more.

Further, in order to improve the adhesion to the silicon wafer, it is possible to copolymerize an aliphatic diamine having a siloxane structure as long as the heat resistance is not reduced. As a preferred specific example Is mentioned.

In the present invention, an adhesion aid may be used to improve the adhesion between a polyimide such as silicon and a semiconductor substrate such as silicon.

As an adhesion aid, an organosilicon compound such as oxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, or an aluminum chelate compound such as aluminum monoethylacetoacetate or aluminum tris (acetylacetonate) or titanium bis (acetylacetonate) ) And the like are preferably used.

Next, an example of a method for forming a passivation film made of polyimide will be described. The polyimide used in the present invention is a method in which a varnish of a polyimide precursor is coated on a silicon wafer, and the polyimide is etched simultaneously with the development of the positive resist using the positive resist as a mask (for example, RADine-Hart, et al., Br. Polym. J. 3, 222 (197
1)) Using a negative resist as a mask and etching the polyimide with an organic alkali such as hydrazine after developing the negative resist (for example, JP-A-53-49701), imparting photosensitivity to the polyimide precursor and directly forming a pattern A passivation film is formed by a forming method (for example, JP-A-54-145794), and holes for wiring are processed. The semiconductor chip thus obtained is sealed with a resin to obtain a product.

The semiconductor chip thus obtained is subjected to transfer molding and resin sealing. Further, post-curing of the sealing resin is performed to obtain a final product.

As a typical sealing resin used for resin sealing of a semiconductor, an epoxy resin-based resin is exemplified. For example, an epoxy resin-based resin is mainly composed of a novolak-based epoxy resin and silica particles. Crosslinking using phenylphosphine and the like can be mentioned. Of course, it is needless to say that various epoxy curing agents and curing catalysts that open the epoxy group upon crosslinking can be used. For this crosslinking, the sealing resin is post-cured. The post-curing temperature can be, for example, about 170 ° C. in the case of the above resin. If the post-cure temperature is too low, the crosslinking reaction does not proceed completely, causing a problem in reliability thereafter. Also, if the post cure temperature is too high,
Deterioration of the sealing resin occurs, causing a problem in reliability. That is, the post-curing temperature is appropriately selected according to the sealing resin used, and the polyimide for forming the passivation film to be used is selected according to the resin.

[Effects of the Invention] As described above, the present invention uses a polyimide having a β dispersion temperature lower than the post-curing temperature of a sealing resin used in a dynamic viscoelasticity measurement for a passivation film for a MOS semiconductor device. Therefore, various disadvantages of the conventional semiconductor device can be solved. That is, the process is simplified and inexpensive, and has a remarkable effect on stabilization of leak current, prevention of wiring corrosion, and prevention of cracks in the interlayer insulating film.

[Measurement of properties] Measurement of dynamic viscoelasticity The measurement of dynamic viscoelasticity in the present invention is performed by measuring a width of 2 mm and a length of 5 cm.
Measure the 4 cm center part of the polyimide film cut into pieces using Orientec's Leo Vibron DDV-II-EA type at a drive frequency of 110 Hz and a heating rate of 2 ° C / min in the range of -150 ° C to 400 ° C. did.

Adhesion strength with sealing resin The adhesion strength with the sealing resin in the present invention was measured by the following method.

(1) A polyimide having a thickness of 2 μm is applied on a silicon wafer and heat-treated up to 350 ° C. is placed on a hot plate at 170 ° C.

(2) Silicon rubber (thickness: 2 mm) reinforced with glass fiber with a hole of 4 mmφ was placed, and a sealing resin (Novolac epoxy resin TH-7006, manufactured by Toray) was embedded therein.

(3) Put a 5kg weight on top of them.
Let stand for minutes.

(4) After cooling, peel off the silicon rubber, 4mmφ, thickness 2
A pad of a sealing resin having a thickness of mm was obtained. This was heat-treated at 170 ° C. for 5 hours to obtain a sample.

(5) Of the samples obtained in (4), a part was at 121 ° C. and 2
A pressure cooker test was performed at atmospheric pressure for 168 hours to obtain a sample.

(6) This sample was measured by a pull-down method (Applied Physics 56, 925, 1987) using Tensilon manufactured by Orientec.

Although the MOS semiconductor passivation method of the present invention is particularly effective for a semiconductor chip having a large area and a multilayer wiring structure, an effective effect can be expected for other resin-encapsulated semiconductor devices.

[Examples] Next, the present invention will be specifically described using examples, but the present invention is not limited thereto.

Example 1 An aluminum wiring having a line and space of 8 μm was mounted on a 9 mm × 9 mm silicon chip, and 1 mol of benzophenonetetracarboxylic dianhydride and 2,2-bis (4-aminophenoxy) diphenylpropane were added. A varnish of a polyimide precursor consisting of 0.96 mol and 0.04 mol of 1,3-bis (3-aminopropyl) -tetramethyldisiloxane is applied so that the film thickness after heat treatment becomes 2 μm, and then 80 ° C. and 200 ° C. , 300 ° C. and 350 ° C. for 30 minutes each in nitrogen. As a result of measuring dynamic viscoelasticity of this polyimide, the peak of α dispersion was 260 ° C., and the peak of β dispersion was 104 ° C.
Met. Further, as a result of measuring the adhesion strength with the sealing resin, the adhesion strength before the PCT test was 5.0 kg / mm ² , and the adhesion strength after the PCT test was 4.5 kg / mm 2.

This chip is packaged in a 16mm x 16mm 48-pin QFP package using a Toray TH-7006 as a sealing resin at a mold temperature of 170 ° C for a molding time of 120 seconds, and then at 170 ° C for 5 hours in a post-cure condition. Was done.

The test sample thus obtained was subjected to a pressure cooker test at 121 ° C. for 500 hours. After the test, the inner chip was opened using fuming nitric acid, and the corrosion state of the aluminum was examined. No corrosion was found. Also, no deformation of the aluminum was observed.

Example 2 A line and space of 8 μm aluminum wiring were mounted on a silicon chip of 9 mm × 9 mm, and 3,3 ′, 4,
From 1 mol of 4'-benzophenonetetracarboxylic dianhydride and 0.96 mol of 2,2-bis (4-aminophenoxy) diphenylhexafluoropropane, 0.04 mol of 1,3-bis (3-aminopropyl) -tetramethyldisiloxane The film thickness after heat treatment of the polyimide precursor varnish becomes 2 μm.
Then, heat treatment was performed in nitrogen at 80 ° C., 200 ° C., 300 ° C. and 350 ° C. for 30 minutes each. As a result of measuring dynamic viscoelasticity of this polyimide, the α dispersion peak was 275.
° C and the peak of β dispersion were 117 ° C. In addition, as a result of measuring the adhesion strength with the sealing resin, the adhesion strength before the PCT test was
4.0 kg / mm ^2, the adhesion strength after the PCT test was 3.5 kg / mm ^2.

This chip is packaged in a 16mm x 16mm 48-pin QFP package using Toray's TH-7006 as a sealing resin, with a mold temperature of 170 ° C and a molding time of 120 seconds, and then with a post-curing condition of 170 ° C for 5 hours. Was done.

The test sample thus obtained was subjected to a pressure cooker test at 121 ° C. for 500 hours. After the test, the inner chip was opened using fuming nitric acid, and the corrosion state of the aluminum was examined. No corrosion was found. Also, no deformation of the aluminum was observed.

Example 3 An aluminum wiring having a line and space of 8 μm was mounted on a 9 mm × 9 mm silicon chip, and 1 mol of diphenylethertetracarboxylic dianhydride and 4,4′-
0.96 mol of diaminodiphenyl ether, 1,3-bis (3-aminopropyl) -tetramethyldisiloxane 0.
A varnish of a polyimide precursor consisting of 04 mol was applied so that the film thickness after heat treatment was 2 μm, and then applied at 80 ° C. and 200 ° C.
Heat treatment was performed in nitrogen at 300 ° C., 300 ° C. and 350 ° C. for 30 minutes each. As a result of measurement of the dynamic viscoelasticity of this polyimide, the peak of α dispersion was 265 ° C., and the peak of β dispersion was 164 ° C. In addition, as a result of measuring the adhesion strength with the sealing resin, the adhesion strength before the PCT test was 3.6 kg / mm ² , and the adhesion strength after the PCT test was 2.4 kg / mm.
It was mm ^2.

This chip is packaged in a 16mm x 16mm 48-pin QFP package using Toray's TH-7006 as a sealing resin, with a mold temperature of 170 ° C and a molding time of 120 seconds, and then with a post-curing condition of 170 ° C for 5 hours. Was done.

The test sample thus obtained was subjected to a pressure cooker test at 121 ° C. for 500 hours. After the test, the inner chip was opened using fuming nitric acid, and the corrosion state of the aluminum was examined. No corrosion was found. Also, no deformation of the aluminum was observed.

Comparative Example 1 An aluminum wiring having a line and space of 8 μm was mounted on a 9 mm × 9 mm silicon chip, and 1 mol of pyromellitic dianhydride was used as an acid component and 4,4 ′ was used as a diamine component.
0.96 mol of diaminodiphenyl ether, 1,3-bis (3-aminopropyl) -tetramethyldisiloxane
A varnish of a polyimide precursor consisting of 04 mol was applied so that the film thickness after heat treatment was 2 μm, and then applied at 80 ° C. and 200 ° C.
Heat treatment was performed in nitrogen at 300 ° C., 300 ° C. and 350 ° C. for 30 minutes each. As a result of the measurement of the dynamic viscoelasticity of this polyimide, no β dispersion peak appeared. In addition, as a result of measuring the adhesion strength with the sealing resin, the adhesion strength before the PCT test was 1.5 kg / mm ² ,
It peeled after the T test.

This chip is packaged in a 16mm x 16mm 48-pin QFP package using Toray's TH-7006 as a sealing resin, with a mold temperature of 170 ° C and a molding time of 120 seconds, and then with a post-curing condition of 170 ° C for 5 hours. Was done.

The test specimen thus obtained was subjected to a preshake cooker test at 121 ° C. for 500 hours. After the test, the internal chip was opened using fuming nitric acid, and the corrosion state of aluminum was examined.
Corrosion had occurred.

Comparative Example 2 An aluminum wiring having a line and space of 8 μm was mounted on a silicon chip having a size of 9 mm × 9 mm, 1 mol of biphenyltetracarboxylic dianhydride as an acid component, and 0.96 mol of paraphenylenediamine as a diamine component. 3-bis (3-aminopropyl) -tetramethyldisiloxane 0.
A varnish of a polyimide precursor consisting of 04 mol was applied so that the film thickness after heat treatment was 2 μm, and then applied at 80 ° C. and 200 ° C.
Heat treatment was performed in nitrogen at 300 ° C., 300 ° C. and 350 ° C. for 30 minutes each. As a result of measuring dynamic viscoelasticity of this polyimide, the peak of α dispersion was 400 ° C. or higher, and the peak of β dispersion was 223 ° C. Also, as a result of measuring the adhesion strength with the sealing resin, the PC
Adhesion strength before T test adhesion strength 1.2kg / mm ^2, PCT after the test was 0.3 kg / mm ^2.

This chip is packaged in a 16mm x 16mm 48-pin QFP package using Toray's TH-7006 as a sealing resin, with a mold temperature of 170 ° C and a molding time of 120 seconds, and then with a post-curing condition of 170 ° C for 5 hours. Was done.

The test sample thus obtained was subjected to a pressure cooker test at 121 ° C. for 500 hours. After the test, the internal chip was opened using fuming nitric acid, and the corrosion state of the aluminum was examined.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-106599 (JP, A) JP-A-62-184025 (JP, A) JP-A-62-253621 (JP, A) JP-A-63-253 193927 (JP, A) JP-A-59-76451 (JP, A) JP-A-63-276045 (JP, A)

Claims (2)

(57) [Claims] 1. A passivation film used in a resin-sealed MOS semiconductor device, wherein said passivation film is made of polyimide, and said polyimide has a main dispersion (α dispersion) and a main dispersion (α dispersion) by dynamic viscoelasticity measurement. Having a subdispersion (β dispersion) occurring at a lower temperature,
A passivation film for a MOS semiconductor device, comprising a polyimide having a β dispersion temperature equal to or lower than a post-curing temperature of a sealing resin. 2. The main dispersion (α dispersion) of the polyimide forming the stress absorbing film according to claim 1 by dynamic viscoelasticity measurement.
And a polyimide having a secondary dispersion (β dispersion) generated at a temperature lower than the main dispersion, 3,4,3 ′, 4′-benzophenonetetracarboxylic acid and 3,4′-diaminodiphenyl ether, 3,4,3 ′, 4'-diphenylethertetracarboxylic acid and 3,4'-diaminodiphenylether, 3,4,3 ', 4'-benzophenonetetracarboxylic acid and 2,2-bis (4-aminophenoxy) diphenylpropane, 3,4,3 ', 4'-Diphenylethertetracarboxylic acid and 2,2-bis (4-aminophenoxy) diphenylpropane, 3,4,3', 4'-benzophenonetetracarboxylic acid and 2,2-bis (4-aminophenoxy) With diphenylhexafluoropropane and 3,4,3 ', 4'-diphenylethertetracarboxylic acid
MO synthesized from at least one selected from 4,4'-diaminodiphenyl ether
S Passivation film for semiconductor devices.